1. Field of the Invention
The present invention relates to a novel lead additive capable of being used inter alia in the glass industry, e.g., in crystal-works, and the ceramic industry, as well as to the process for its production.
2. Description of the Prior Art
The glass and ceramic industries currently use lead oxides, minium and/or litharge, which are powdery products the particles of which generally have a diameter of less than 40 microns. Because of their scattering and dusting, in the course of handling, e.g., as batches are prepared and placed in the furnace, use of such products involves significant risks of atmospheric pollution. This may cause lead-poisoning problems in the users of these powdery lead oxides.
It has often been proposed to agglomerate these powdery products through use of a bonding agent so as to obtain granules which would be easier to handle. As bonding agents, water and silicates as are employed in the composition of glases and ceramics have been used, among others.
Thus French patent application No. 2,300,743 describes a process for producing minium granules of a particle size of between 0.5 and 5 mm. These are prepared by introducing minium powder into a granulator consisting of a rotating tank which is open at the top and inclined with respect to the vertical axis, and pulverizing an aqueous solution of potassium silicate in this tank. The proportion of potassium silicate in the granules may vary between 2.5 and 5% by weight, preferably between 3 and 4.5%.
Other granules are prepared using water as the binder, but these produce dust during handling. In addition, their abrasion resistance is low.
None of these agglomerates are entirely satisfactory, either because their granulometry causes segregation effects upon mixing with other constituents of the batch and upon fusion, or because too much dust is produced during handling.
One object of the present invention is therefore to provide a new lead additive, particularly for the glass and ceramics industries, presented in the form of granules having greater abrasion resistance than presently known products and a granulometry similar to that of other components of the batch in which the new additive is used.
An additional object of the invention is a new lead additive which does not involve the production of dusts during handling, which dusts are a source of pollution and often of lead poisoning.
One purpose of the present invention is to provide a process enabling production of this novel lead additive in the form of granules which do not produce dust during handling, the granules having good abrasion resistance and a granulometric distribution adapted to that of the other components of the batches in which it is used.
An additional purpose of the invention is to provide a process enabling production of granules of irregular shape.
Another purpose of the invention is to provide a process eventually enabling direct production of this new lead additive in the form of granules of desired sizes, i.e., without the need for subsequent grinding.
An additional purpose of the invention is to provide a process enabling production of granules of either primary lead oxides, litharge, minium, or their mixtures.
Further objects, purposes and advantages of the present invention will become apparent upon reading the undergoing specification and claims.